A medical endoscope is an instrument used to inspect the inside of a body. A typical endoscope has a distal end comprising an optical or electronic imaging system, a proximal end with controls for manipulating the tool and devices for viewing the image, and a solid or tubular elongate shaft connecting the ends. To use an endoscope, a physician inserts the distal end into a patient through a natural orifice or an artificial incision and then pushes the shaft into the patient until the distal end reaches a site of interest. The proximal end remains outside the patient and typically connects to an eyepiece, video monitor, or other equipment. Some endoscopes let the physician pass tools or treatments down a hollow channel, for example, to resect tissue or retrieve objects. Other endoscopes are strictly inspection devices and not used for remote procedures.
After an endoscope is used on a particular patient, the endoscope must be sterilized before it can be used again. The goal of sterilization is to remove all foreign matter and all pathogens. A traditional method for sterilizing metallic surgical instruments is to place them in a device called an autoclave. An autoclave is a strong, enclosed pressure vessel with a heater and a pressure-tight door. An autoclave heats its contents with pressurized steam to a high temperature, above the boiling point of water, killing pathogens and microorganisms.
The high temperature and pressure within an autoclave can damage or degrade endoscopes and similar instruments, however. As endoscopes have become more sophisticated and costly, it has become more important to reduce or prevent this damage and degradation while continuing to rely on an autoclave for positive sterilization.
A typical electronic endoscope may contain circuit boards, integrated circuits, conductors, connectors, lenses, prisms, image sensors, and so on. A typical endoscope protects these internal parts, for example, during sterilization, through a sealing system based on O-rings, silicone seals, epoxy seals, or similar flexible, semi-flexible, or adhesive sealants. Unfortunately, some of these sealing methods cannot withstand repeated exposure to pressurized steam in an autoclave or to other sterilization conditions. Sterilization procedures for endoscopes commonly start with partial or total disassembly followed by sterilization by immersion in sterilant gasses, liquids, or plasmas. These sterilization procedures are labor-intensive and expensive. Worse, they are not always totally effective at disinfecting and decontaminating the instrument. Disease-causing microorganisms may survive processing, creating a risk of iatrogenic infection to subsequent patients—a complication that contributes to extended hospital stays and increased mortality and morbidity.
What is needed is an electronic endoscope that can withstand rigorous sterilization in an autoclave—which, by necessity and design, creates a very harsh environment. Ideally, the endoscope would not require significant disassembly prior to autoclaving. Ideally, it would survive repeated autoclaving without damage or degradation. Some attempts have been made to provide hermetic enclosures. For example, U.S. Pat. No. 6,572,537 discloses an endoscope having a solid-state image pickup device with a distal tip sapphire window and a sapphire rear end cover. The cover and window are subjected to a metallization process and then joined by an airtight brazing process to metal members to form a hermetic seal. Soldered or brazed connections are used in various other places in the device to form hermetic seals. (See also U.S. Pat. Nos. 6,716,161; 6,547,722; 6,547,721; 6,425,857; 6,328,691; 6,146,326; 6,080,101; 6,030,339; 5,868,664; 5,810,713; 5,188,094; and 4,878,485). All the foregoing patents are hereby incorporated by reference, as if set forth herein in their entireties.
Unfortunately, the foregoing needs have not been met by the prior art because the mere design of a hermetic enclosure, which might be capable of withstanding harsh environmental conditions, does not automatically satisfy other functional and operational needs. In particular, different parts of an endoscope ideally require different material attributes. Some desirable materials that can withstand harsh conditions may not easily join to other desirable materials. This is certainly the case relative to, for example, aluminum, stainless steel, and titanium metals, or their alloys, each of which may provide desirable operational or functional attributes.
More specifically, the need to join dissimilar metals partly results from the part-by-part selection of materials guided by the purpose of each part and the properties of the available metals and alloys. The parts of medical instruments that actually enter a patient's body are often made from stainless steel, an FDA-approved material with corrosion-resistant properties desirable for maintaining a sterile surface. Stainless steel has poor heat conductivity and is relatively heavy, however. Aluminum, in contrast, has excellent heat conductivity, making it a preferred material for the parts of medical instruments that contain heat sources such as electrical or electronic devices. Aluminum is also lighter than stainless steel, making it better for large parts, especially those require that precise manipulation. Aluminum is unfortunately prone to oxidation, making it non-ideal for parts that pass into the body; and aluminum is relatively soft, making it non-ideal for parts exposed to friction, scratching, and wear. Titanium, on the other hand, is exceptionally strong, hard, and tough, making it preferential for parts exposed to friction and wear. As a result of its toughness, titanium traditionally has been difficult to machine, so that titanium parts have been expensive. Ongoing improvements in metalworking technologies have lead to an ongoing expansion of the use of titanium in medical instruments and elsewhere.
Producing a hermetic enclosure greatly benefits from the ability to form fused joints such as welds. Dissimilar metals such as stainless steel, aluminum, and titanium are difficult or impossible to weld to each other via laser welding, arc welding, and similar techniques, however. One approach would be to manufacture all structural components from compatible metals or alloys. For example, the structural parts of the objective head, shaft, and handle all might be made from stainless steel, facilitating the formation of fused joints. This approach precludes the part-by-part selection of metals and alloys, a considerable drawback. Fusing optical glasses used in objective heads presents similar challenges.